This invention relates in general to xerography and more specifically to a novel photosensitive device.
In the art of more or less conventional xerography, a xerographic plate containing a photoconductive insulating layer is imaged by first uniformly electrostatically charging its surface. The plate is then exposed to a pattern of activating electromagnetic radiation such as light, which selectively dissipates charge in the illuminated areas of the photoconductive insulator resulting in a latent electrostatic image corresponding to the pattern of light-struck and nonlight-struck areas. The latent electrostatic image may then be developed to form a visible image by depositing finely divided electroscopic marking particles on the surface of the photoconductive insulating layer.
In recent years, interest has been shown in flexible electrophotographic plates for use in high speed office copying machines. Some of these plates are multilayered devices comprising, a conductive substrate, an adhesive blocking interface layer, a charge generation layer and a charge transport layer. The charge transport layer comprises an organic charge transport molecule dissolved or dispersed in a polymeric matrix material. This layer is substantially nonabsorbing in the spectral region of intended use, i.e. visible light, but is "active" in that it allows (1) injection of photogenerated charge from the charge generation layer and (2) efficient transport of these charges to the surface of the transport layer to discharge a surface charge thereon.
One of the parameters limiting the performance of these structures is the charge carrier mobility in the charge transport layer. When a structure such as this is employed in the above-described xerographic process, during the exposure step light is absorbed in the photogenerator layer creating free charge carriers. These charge carriers are then injected into and transported across the charge transport layer to the surface thereof. The charge carrier mobility or the velocity determines the time of transit across the transport layer. The maximum discharge of the light exposed area is obtained if the injected charge carrier has completely traversed the transport layer before the photoreceptor belt arrives at the development station. In materials with low charge carrier mobilities, the carrier will be part way through the charge transport layer when the photoreceptor belt arrives at the development station giving rise to less than maximum discharge of the photoreceptor.
The art is constantly searching for charge transport layers having high carrier mobility so that the time between exposure and development can be reduced without sacrificing xerographic efficiency. By reducing this time period, faster machines are possible.